The Varkala Tunnel System, also known as the Varkala Canal or Varkala Thurapp in local dialect, is a system of tunnels situated in the municipality of Varkala of Trivandrum, Kerala, India. It is one of the region's most important historic sites and architectural marvels. This site was constructed by the Travancore Kingdom to establish a continuous inland waterway across Thiruvithamkoor as TS Canal, which was meant to serve as a trade route. The construction of the two long tunnels was started in 1867 and work on the first was finished in 1877, while the second was completed in 1880.

With a length of 1,069.848 metres (0.664773 mi), the two tunnels played a vital role in transferring ferry goods and people from the capital city of Trivandrum to Kollam during the pre-independence era. The tunnel is located under the main cliff of the region and represents the architectural excellence of the workers and engineers of that era.

Built under the supervision of then chief engineer Walthew Clarence Barton during reign of T. Madhava Rao, the Dewan of the Travancore Kingdom, the tunnel also makes up for the major man made reach i.e. Varkala stretch of Thiruvananthapuram–Shoranur canal, which passes through a delicate geological structure. In 1934 -1942 period the walls of the tunnel got a concrete lining.

The tunnel is built in an area famous for its Cenozoic sedimentary formation cliffs, a unique geological feature on the otherwise flat Kerala coast, which are known among geologists as Varkala Formation. The tunnels are carved through Laterite rocks.

There are two tunnels in the system, namely:

• Sivagiri Passage 722 m long; and
• Chilakkoor Passage 350 m long.

The tunnel system connects the Anchuthengu Kayal with the Edava-Nadayara Kayal.

Despite the potential for tourism, the passages remain unused. It is silted and maintenance works are in limbo. Around 2006, there was renewed interest in reviving the tunnels by then-Chief minister of Kerala, Shri. V. S. Achuthanandan, who undertook a boat ride in the canal to make a first-hand assessment. Thereafter it remained in limbo until 2014 -16 period, when discussions restarted, though these soon broke down. In 2016, the state government sought the help of civil engineer E. Sreedharan to revive the tunnel.

In 2017, discussions were held regarding the construction of a new waterway bypass, skipping existing tunnels due to lack of width and draft as per National Waterways standards.

As of 2020, in Chilakkoor passage, dredging work and sledge removal are progressing. Work on Sivagiri passage is also expected to start soon. The passages are planned to be used for tourist activities.

The Government of India has turned down Kerala's demand to extend the existing National Waterway 3 route to Kovalam from Kollam through Varkala.

• Waterways transport in Kerala
• TS Canal
• AVM Canal
• Kollam Canal